A liquid crystal display comprises a polarizing plate and a liquid crystal cell. Various display modes of the liquid crystal cell have been proposed, for example TN mode and STN mode, which are now popularly used. In a liquid crystal display of TN or STN mode, an optical compensatory sheet is generally provided between the polarizing plate and the liquid crystal cell to improve the viewing angle and qualities of the displayed image.
U.S. Pat. Nos. 4,583,825 and 5,410,422 disclose a liquid crystal display comprising a liquid crystal cell of OCB (Optically Compensatory Bend) mode, in which alignment of rod-like liquid crystal molecules in upper part is essentially reversal (symmetrical) to the alignment of molecules in lower part. Since the liquid crystal molecules are symmetrically aligned in the upper and lower parts, the liquid crystal cell has a self-optical compensatory function. Therefore, this mode is referred to as OCB (optically compensatory bend) mode. In addition to the self-optical compensatory function, the liquid crystal display of OCB mode has another advantage of a rapid response.
Japanese Patent Provisional Publication No. 2(1990)-176625 discloses a liquid crystal display comprising a liquid crystal cell of VA (Vertical Alignment) mode, in which rod-like liquid crystal molecules are essentially vertically aligned while voltage is not applied (while normally black) and the molecules are essentially horizontally aligned while voltage is applied. The liquid crystal display of VA mode has advantages of giving an image with high contrast, responding rapidly and preventing the image from undesired coloring.
As described above, the liquid crystal displays of OCB and VA modes have excellent characters in displaying images, as compared with popularly used displays of TN and STN modes. Nevertheless, in consideration of images given by a CRT display, it is still necessary to improve the displays of OCB and VA modes.
In the displays of OCB and VA modes, as well as in those of TN and STN modes, optical compensatory sheets may be used to improve displayed images.
Japanese Patent Provisional Publication No. 09(1997)-197397 (U.S. Pat. No. 5,805,253) and PCT Publication No. 96/37804 (European Patent Publication No. 0,783,128) disclose a liquid crystal display of OCB mode equipped with an optical compensatory sheet comprising discotic liquid crystal compound. The optical compensatory sheet remarkably improves the viewing angle of the liquid crystal display of OCB mode.
Japanese Patent Provisional Publication No. 2001-027706 discloses a liquid crystal display of VA mode equipped with an optical compensatory sheet comprising discotic liquid crystal compound.
However, though improving image qualities, the optical compensatory sheet provided between the liquid crystal cell and the polarizing plate generally thickens the display. Further, such display is easily distorted by heat to leak light since the compensatory sheet increases elements constituting the display.
Japanese Patent Provisional Publication No. 11(1999) 316378 discloses an elliptically polarizing plate for OCB mode (or for horizontal alignment mode) in which an optical compensatory sheet and a polarizing plate are unified. In detail, the optical compensatory sheet comprises a transparent support and a thereon-provided optically anisotropic layer formed from discotic liquid crystal compound, and works also as a transparent protective film of the polarizing plate. The thus-unified polarizing plate improves displayed images without thickening the display.
However, it is difficult for even the unified polarizing plate to fully prevent large displays of 17-inches or more (which have recently been produced and used) from thermal distortion and accordingly from leaking light.